1. Technical Field
The present invention relates to a wireless local area network (WLAN) network and a channel selection method of a WLAN station, and more particularly to a channel selection method of a WLAN station in which a station entering a WLAN service area determines an access channel in consideration of the load of each service channel provided from at least one access point (AP).
2. Related Art
A wireless local area network (WLAN) is also referred to as Wi-Fi, meaning that it makes the wireless network convenient to use like a Hi-Fi audio component. Personal digital assistants (PDAs) or notebook computers can use very high speed Internet within a specific area about an access point (AP). In this case, the PDAs or notebook computers do not require a telephone line or a private line because they use radio frequency, but they require a WLAN card.
Although the WLAN was initially industrialized in the late 1980s by wireless appliance manufacturers such as Proxim, Symbol and so on, it could not have become generalized because many types of formats there of were jumbled up. However, it has developed rapidly after the Wireless Ethernet Capability Alliance (WECA), which was changed into WiFi in 2002, assigned WiFi authentication in September 1999 to products compatible with a standard, IEEE 802.11b, that the WECA had proposed. It was introduced into the Republic Of Korea in 2000, and has been activated in universities and companies.
IEEE 802.11 WLAN initially supported a data transfer rate of 2 Mbps using 2.4 GHz band, but with the determination of a physical layer standard for IEEE 802.11b and IEEE 802.11a in 1999, IEEE 801.11b supported a data transfer rate of 11 Mbps in the 2.4 GHz band and IEEE 802.11a supported a data transfer rate of 54 Mbps in the 5 GHz band. In particular, IEEE 802.11a adopted Orthogonal Frequency Division Multiplexing (OFDM) with 52 sub-carriers in order to obtain a high transfer rate, so that it had a strong advantage against multi-route interference because of simple equalization. Then, IEEE 802.11g as a high speed transfer standard for 2.4 GHz band was completed, and it adopted a Complementary Code Keying-OFDM (CCK-OFDM) as a compulsory transfer manner for interoperating with the IEEE 802.1b.
There are two modes of configuring WLAN. One is an ad-hoc mode, and the other is an infrastructure mode. The ad-hoc mode is a mode in which a local area network (LAN) is configured by wireless appliances only without a central controller or access points. The respective wireless appliances communicate directly with other appliances without a central controller. This is advantageous in the case where there is no need for microcomputers to be gathered together at one place in order to communicate with other networks.
Conversely, the infrastructure mode is one in which access points (APs) are configured to expand the existing cable LAN into a wireless device. The APs function as a central controller of the WLAN by connecting the wire and WLANs together. The APs control transmitting and receiving between the plurality of wireless devices within a specified area. Even in the case of a hot spot environment, wherein many users gather in crowds within a restricted space, the infrastructure mode is mostly adopted as a base mode. In the infrastructure mode for 802.11 WLAN communications, a station (laptop, smart device, and so on) first checks the connectable AP and network in such a way that it monitors a ‘beacon’ frame which generates a signal by which the AP reports its existence, or it probes a specified network using a ‘probe’ frame.
A channel selection algorithm scans a given channel set from its lowest channel to its highest channel in such a manner that it selects the fastest channel which is now serviced by an AP, or the channel with the highest received signal strength indication (RSSI) by scanning all of the channels. This procedure is implemented whenever a new station has access, and continues until the number of stations exceeds the maximum number that one AP can control, so that the corresponding station cannot control more stations. In this case, the next access station is brought over to the AP which services the next channel.
The network load or traffic between APs should be maintained properly in order to provide services to as many stations as possible, and to maintain good service quality as well. To this end, it is required that the mobile station select the AP with least load before it actually has access to the WLAN system. However, as seen before, it is difficult for the presently used algorithm to realize this.
Thus, there is a need for a channel selection method which can properly distribute a network load over the respective APs, and which can provide good service quality as well.